Method and apparatus for blending pulverulent materials



Nov. 5, 1968 E. J. KELLY 3,409,273

METHOD AND APPARATUS FOR BLENDING PULVERULENT MATERIALS Filed Nov. 17,1967 INVENTOE. Enema 1]. KELLS/ United States Patent O" 3,409,273 METHODANDAPPARATUS FOR, BLENDING PULVERULENT MATERIALS Edgar -J. Kelly, LakeZurich, IIL, assignorto American Colloid Company, Skoki e, Ill.,acorporation of Delaware g Filed Nov. 17, 19 67, Ser. No. 683,956

' 7 Claims. (Cl. 259 -4) ABSTRACT OF THE. DISCLOSURE A method andapparatus for mixing pulverulent or finely-divided materials byfiuidizing such materials to reduce the friction between the particlessoas to facilitate combining, and recirculating such fluidized materialswithin an enclosed container so as to'effect complete blending andmixing thereof, permitting discharge' of unsegregated material. 7

Pulverulent or granular materials, such as clays, cements, crushedminerals, coal, etc. are generally composed of particles which differ insize and when a silo or hopper is being filled, larger or coarseparticles tend to separate from finer particles. Such segregationresults in the initial discharge of material high in fines and a laterdischarge high in coarse particles, whereas constancy and homogeneity isdesired and often essential. Mixing devices have been proposed in theprior art which attempted to 3,409,273 Patented Nov. 5, 1968 flow pathof fluidized pulverulent material particles and recirculating suchfluidized material by aspirating means.

Another object of the present invention is to blend pulverulentmaterials with an apparatus having zones or regions of varying pressurewithin a substantially cylindrical container and having stationarymechanical means disposed within the container for controlling the flowpath of the fluidized material.

Still another object of the present invention is to blend finelydivided, powdered or granular material either continuously or by a batchprocess selected by controlling the obtain homogeneity of a singlematerial or a plurality of materials, but such devices were expensive,generally capable of handling only small batches and not satisfactory.The use of stirring arms with and without injected air and the use ofair alone in specialized constructions have been tried. Generally, theair was supplied at high pressure thereby increasing the cost, and themode of operation of these prior devices was not capable of producingsatisfactory results.

'It has been found that the particular interior configuration ofblenders or hoppers is critical to obtaining a satisfactory mix of thematerial. In the prior art, the use of nozzles positioned in the lowerportion of a container or hopper so as to discharge air under highpressure'has been tried in an attempt to create vortices within thecontainer or hopper so as to effect satisfactory blending. However,there are disadvantages to such prior art devices caused by theturbulence created within the container due to the introduction of highpressure air and difliculty in controlling the flow path of thefluidized material within the container due to such air turbulence.

The present invention provides 'an inexpensive apparatus of largecapacity, which may be used to continuously blend and discharge materialat exemplary rates of 400 to 600 tons per hour (or in batches of, forexample, 30-40 tons each), the apparatus being capable of being usedeither as a silo or storage container or a blender or both. Segregationof coarse and fine material components is prevented by a novel mode ofoperation including tangential feed into the upper portion of anenclosed chamber, and the movement of the material in a series ofsuccessive inwardly contracting and outwardly expanding spirals to thelower portion of the chamber, followed by axial and upward return forrecirculation and effective mixing. The repeated reversal in thedirection of movement of the material (inwardly, outwardly, up and down)is facilitated by the use of an aspirator for the upward movement of thematerial, the presence of air fiuidizing the material and permitting alarge tonnage to be mixed within a very short period of time.

Accordingly, it is a general object of the present invenvolumetric orweight rate of flow of materials into an enclosed container relative tothe volumetric rate of flow of air supplied to aspirating means used forrecirculating and fiuidizing material.

A further object of' the present invention is to mix pulverulentmaterial within a container by introducing material into the upperportion of the container by air transport in a tangential direction andblending such material by controlling the downward flow of the fluidizedmaterial and recirculating such material by aspirating means.

Other objects and advantages of this invention will be readily apparentin the following description when considered in connection with theappended drawings.

In the drawings:

FIG. 1 is a side elevation sectional view of an apparatus for blendingpulverulent material constructed in accordance with the presentinvention;

FIG. 2 is a top plan view of the apparatus as shown in FIG. 1, with aportion thereof shown in section;

FIG. 3 is a top plan view of a portion of the apparatus shown in FIG. 1,taken along the line 3-'-3; and

- FIG. 4 is a side elevation sectional view taken along the line 44 ofFIG. 3.

The exemplary form of apparatus of this invention shown in the appendeddrawings is illustrated by the blender and container 10 which comprisesan upper cylindrical portion indicated at 11 and a lower portion 12 inthe form of an inverted truncated cone, 'this inverted truncated conebeing connected to the upper cylindrical portion 11. The lower ordischarge portion of the cone 12 is preferably provided with a valvedmaterial outlet indicated at 13; the top of the container 10 is providedwith a top wall 14 having a central aperture in which there is held aremovably attachable, inwardly extending deflector 15 having a conicallower surface 16. Another aperture in the top wall 14 is incommunication with a vent pipe 17 which may lead to the atmosphere or toa small dust collector (not shown).

The periphery of the upper cylindrical portion 11, adjacent the top wall14, is provided with a tangential material inlet 18. It is to beunderstood that the material supplied to the mixer and blender 10 may beintroduced in airborne suspension or the material may be supplied to theblender by gravity or any other means. Pulverate material supplied byair transport is most often employed and therefore inlet line 18 isshown provided with a manually adjustable valve 19, shown in FIG. 2. Itmay also be noted that the inner surface of the cylindrical portion 11immediately adjacent the inlet may be lined with a wear pad 20, suchwear pad extending for 60-120 of the arc of. the portion 11.

To facilitate blending and eliminate segregation of the particulatepulverulent or granular material being blended, means are provided forcontrolling and reversing the downward movement of the materialsupplied. As

shown best in FIG. 1, the blender is provided with an invertedtruncated, conical baflie 21 the upper edge 22 of the baflie beingattached to the inner surface of upper cylindrical portion 11 slightlybelow the level of the inlet pipe 18. The lower edge 23 of the baflie 21opens downwardly. Very good results have been obtained when the diameterof the baflie 21 at its lower or discharge edge 23 is on the order of0.4 to 0.6 D, where D represents the diameter of the upper cylindricalportion 11 of the blender. The inwardly and downwardly extendingdirectional baflie 21 is maintained in a position by three or morestruts, one of which is indicated at 24, the struts being welded orotherwise suitably attached to the walls of the blender and to thebaflie.

It will be understood that the upper or inner surface of the baffle 21directs the incoming pulverulent material towards the center of theblender. Material so directed in a constricting spiral path is thendeflected by a second conical baflie 25 (shown held in position bystruts, one of which is shown at 26), the upper surface of the baffle 25being virtually normal to the upper surface of baflle 21 but spacedtherefrom, thereby causing the material to be reversed in its directionof downward flow in an expanding spiral towards the inner surface of thelower, inverted cone portion 12 of the blender. Again it has been foundthat very eflective operation is obtained when the diameter of the lowermarginal edge 27 of bafiie 25 is on the order of from about 0.4 to 0.6D. The conical baflie 25 may be welded or suitably attached at its upperend to the outer wall of aspirator pipe section 34.

It may be observed that by the construction described. whether theincoming pulverulent material is fed by gravity or in airbornesuspension, the incoming material is caused to swirl and cascadedownwardly, reversing its direction from the external areas of theblender towards the center and then again to the outside and againtowards the center. The normal tendency of coarse particles to findtheir way to the sides of the hopper or container are thus repeatedlythwarted and an effective mixing of coarse and fine particles isobtained.

The blender 10 is also provided with additional mixing and aspiratingmeans which repetitively circulates the material within the blender andfacilitates discharge of a homogeneous mixture of particulate materialdiffering in particle size. Such additional aspirating and mixing meanscomprise the air inlet pipe 28 extending through the lowermost portionof cone portion 12 and terminating in the vertically and centrallyoriented nozzle 29 whose upwardly directed open end is of smallerdiameter than the pipe 28.

The pipe 28 is preferably supplied with air at a relatively lowpressure, for example, to pounds per square inch gauge, but insuflicient quantity ot fluidize the pulverulent material, the volumetricrate of flow of air being controlled through a valve 30. The upwardlydirected converging nozzle 29 is positioned and spaced in operativerelation to a shroud 31 carried by the lower end of an aspirating pipe32 which, in turn, is connected by an expanding conical pipe section 33to the upstanding axial pipe section 34 which terminates below theconical deflecting surface 16 of the deflector carried by the top wall14 of the blender. Preferably, the upper or discharge portion 35 of theaspirator pipe section 34 is below the level of the supply inlet pipe 18and approximately at or slightly above the upper edge 22 of the baflie21, as illustrated.

It will be noted that the upper open end of nozzle 29 is in spacedrelation with the inner walls of the shroud 31 whereby the velocity oftheincoming air, together with the reduced pressure caused by suchvelocity, aspirates or sucks in the material contained in the lowerportion of cone 12 and causes such material to be conveyed upwardlythrough the aspirator pipe section 34 and discharged upwardly againstthe conical lower deflecting surface 16, thereby spreading the fluidizedmaterial radially in the upper end of th cylindrical portion 11 of theblender. The aspirating pipe sections may be supported from the walls ofthe blender by means of struts, one of such struts being indicated at36.

Disposed below baflle 25 is means to maintain the flow path of fluidizedmaterial near the inner wall of the lower cone portion 12 of theblender, indicated generally by the reference numeral 37. Flow pathcontrol means 37 comprises a gas pressure inlet manifold pipe 38connected to a gas pressure source (not shown) located exteriorly ofcontainer 10 through an air flow control valve 39. The flow path controlmeans 37 also includes a plurality of toroidal gas discharge pipes 40,each of which has a plurality of radially inwardly directed dischargeopenings 41, as seen best in FIGS. 3 and 4.

The flow path control means 37 will create a gas pressure zone in thelower cone portion 12 of the blender 10 which exceeds the ambientpressure within the container so that the spiraling cascadingpulverulent material passing into the upper end of lower cone portion 12will be forced to flow in the peripheral area adjacent the inner wallthereof. To prevent the fluidized material, particularly the more coarseparticles of such material, from adhering to the inner wall of the lowercone portion 12 of the container, a plurality of fluid injecting pads 42may be positioned around the periphery of the inner walls of this lowerportion of the container. Each of the fluid pads 42 are connectedthrough a coupling to an external gas supply source (not shown).

In operation, pulverulent material is introduced into the blender 10,preferably by air transport through the material supply inlet pipe 18 byopening valve 19 disposed in such pipe. As mentioned above, the materialmay also be fed into the blender 10 through gravity feed into theperipheral upper end of the upper cylindrical portion 11 of the blender.Simultaneously with the introduction of the pulverulent material, valve30 in air inlet pipe 28 is opened so that a relatively high velocity,but low pressure, stream of air is introduced into the blender throughthe recirculation pipe section 34 into the upper portion of the blender.The air discharged from the upper end 35 of recirculator pipe section 34will impinge upon reflector 16 and spread radially through the upper endof the cylindrical portion 11. Since the pulverulent material isintroduced in a tangential direction the material will combine with theradially discharged air so as to form a confluent flow of fluidizedpulverulent material moving in a downwardly spiraling direction guidedby the baflle 21 towards the center of the blender.

This downward spiraling stream of fluidized material contracts until itpasses through the lower opening 23 of battle 21 and is then expandedand directed by baflle 25 into the upper end of the lower conicalportion 12 of the blender. The cascading flow of pulverulent materialwill continue proximate the inner wall of the lower portion 12 of theblender towards the central region in which the aspirating means ispositioned by virtue of the higher pressure gas zone created by the flowdirecting means 37. The fluidized material continues toward thedischarge opening in the lowermost end of the cone portion 12, but as itapproaches the region of the aspirating means the material will be drawnor sucked into the aspirating means due to the low pressure regionexisting at the discharge end of the inlet nozzle 29. In this manner,the material will be further fluidized and recirculated to the upper endof the blender 10 through the recirculation pipe section 34.

It will be appreciated that the blender 10 may be operated so as to mixmaterials either continuously or by a batch method. The weight rate offlow of pulverulent material into the blender through inlet pipe 18 maybe selected by means of control valve 19. The volumetric rate of airflow introduced into the blender will also be controlled by selectiveoperation of air inlet control valve 30. The amount of pulverulentmaterial which will collect at the discharge opening of the blender willthus be controlled by balancing the amount of material introduced withthe amount of air introduced so thatall, or a portion thereof, may beaspirated and'continuously'recirculated within the container. Inoperation as a'batch method, theiamo'unt of air introduced will besufficient so as to continuously" recirculate all materialintroducedinto the blender, for a given period ofgtime, and the discharge openingof the blender will be closed. To o'pi'ate continuously,'-'the' amountof 'material introduced relative to the amount of air introducedinto theblender w ill be controlled so that a "pertain-or the pulverulentmaterial will continuously collect at the-discharge opening of the f Iblender, which will be open, so that the blended ,unsegregated combinedmaterial may be exhausted. I

' An actual example ofuse, of the above-described embodiment of the invention will demonstrate the novel blending effectiveness oftheapparatus. Approximately two hundred tons o f powdered bentonite clay,having a nominal classification of ninety perc'ent 'less 'than"2'0'0mesh and a bulk density of 55 lbs. per cubic foot, was fed into theapparatus for blending. Sieve analysis indicated that the pulverulentbentonite was one hundred percent less than 150 mesh, ninety percentless than 200 mesh, and five percent less than 325 mesh. Furthermore,bentonite has the property of imparting viscosity to a water solutionbut natural bentonite clay, i.e. as it is mined, has a great variationin viscosity. This particular bentonite material had a natural unblendedviscosity range of from 3 cps. to 26 cps. in a 6%% concentration.

In blending the bentonite by batch process, 650 cubic feet per minute ofair was introduced through the mixing and aspirating means at 6 p.s.i.g.Since the entire charge of pulverulent material was fed into thecontainer prior to commencing blending, the material head required 18p.s.i.g. in the air inlet pipe to overcome the head. However, thepressure required for operation shortly dropped to 6 p.s.i.g. The mixingand aspirating means with this volumetric rate of flow produced arecirculation rate of 600 tons per hour and, for this particularpulverulent material, it was found that ten recirculation cycles yieldeda well-blended homogeneous material of differing particle size.

Specifically, sieve analysis of the blended material showed a uniformhomogeneous mixture of particle sizes and a viscosity of 13 cps. in a 6A% concentration.

The above-described material was also used in a test of the apparatus incontinuous operation. The container was fed at a rate of fifty tons perhour and the lower portion of the container was allowed to fill to adesirable level by closing the discharge opening. The mixing andaspirating means was operated so as to allow the level of blendedmaterial to be maintained after the discharge opening was openedproviding a continuous operation. The same uniform homogeneous mixtureof blended material was obtained.

In another example of use of this apparatus for both storage andblending, a fifty ton container was filled with silica sand weighing 100lbs. per cubic foot, and having a No. 90 grain fineness according toAmerican Foundry Society standards. Without blending, it was found thatthe container when discharged would initially deliver material high infines and subsequently the coarse part of the material.

However, when the apparatus was operated with 900 cubic feet per minuteintroduced through the mixing and aspiratin g means :at a startingpressure of 22 p.s.i.g. and an operating pressure of 7 p.s.i. g., ahomogeneous mixture was discharged with the grain size graduationconsistently plus or minus one-half of one percent.

It will be appreciated from these examples that the present inventionprovides a blending and storage apparatus of large capacity which bycontrolled movement of the material will provide an unsegregated,homogeneous, uniform mixture of pulverulent material. It will thereforebe seen that many modifications and variations of the present method andapparatus for blending pulver ulent materialsare possible in light ofthe. above teachings. It is therefore to be understood that within thescope of the appended claims, the invention may be practiced otherwisethan specifically described.

I claim: i p 1. A method for producing, storing and discharginghomogeneous mixtures of finely divided solid materials comprising thesteps of:

introducing finely divided solid material by air transport into theupper end of a cylindrical portion of a container in a tangentialdirection to create a circumferential flow path of the material;directing low pressure air flow radially in the upper end of thecylindrical portion of the container to create a confluent flow path offluidized material; H directing the' flow of the fluidized material in adownward spiral path toward the axis of the container cylindricalportion;

re-directin g the downward spiralling flow of fluidized material awayfrom the axis of the container and into the upper end of an invertedcone portion of the container;

reversing the flow of down-ward spiralling fluidized material toward thecontainer axis;

aspirating the fluidized material in the lower region of the invertedcone portion of the container; and

re-circulating the aspirated fluidized material to the upper end of thecylindrical portion of the container to effect complete homogeneousblending of the finely divided solid materials.

2. An apparatus for producing, storing and discharging homogeneousmixtures of finely divided solid material comprising:

-a container housing having an upper cylindrical portion provided with atop wall and a lower inverted cone portion with a discharge opening atthe lower end thereof;

a tangential material inlet means in the periphery of the upper end ofthe cylindrical portion adjacent said top wall;

means within said container housing for reversing the direction ofdownward movement of the material by a series of successively inwardlycontracting and outwardly expanding spirals to the lower portion of saidhousing, said means comprising an upper inverted truncated conical bathein said cylindrical portion extending from a zone slightly below saidmaterial inlet means and providing a surface for guiding material towardthe central axis,

and a lower conical baflle providing a surface adapted to receivematerial from the upper truncated conical bafile and guide material awayfrom the central axis toward the lower portion of the container housing;

axially positioned, upwardly directed aspirating means in the lowerportion of the lower section of the housing, a pipe plositioned inoperative vertical axial alignment with said aspirating means andextending through said housiing lower cone portion to the upper end ofthe cylindrical portion of the housing;

and means for supplying low pressure air to said aspirating means tocirculate material from the lower portion of the housing to the upperportion thereof.

3. The apparatus of claim 2 wherein said tangential material inlet meansincludes means providing air transport of such material into thecontainer.

4. The apparatus of claim 3 additionally including means supported inthe lower inverted cone portion of the housing for creating a pressurezone exceeding the housing ambient pressure so as to direct the downwardmovement of the material outwardly toward the wall of the housing lowerportion.

7 5. The apparatus of claim 4 additionally comprising: valve means inoperative relation with the tangential material inlet means forselectively controlling the weight rate of material flow introduced; and

valve means in operative relation with the low pressure air supply meansfor selectively controlling the volumetric rate of air flow introduced,

whereby a selected portion of the downward flow of material may beaspirated and the remainder collected in the lower end of the lowerinverted cone portion of the container.

6. The apparatus of claim 5 wherein the lower opening of the upperinverted truncated conical baffle is between 0.4 and 0.6 of the diameterof the upper cylindrical portion of the container and the lower edge ofthe lower conical bafile has a diameter no less than the diameter of thelower opening of the upper inverted truncated conical 'baffie.

7. The apparatus of claim 6 additionally comprising:

means for providing a fluidized bed of gas on the inner wall of thelower inverted cone portion of the container so as to prevent thematerial from adhering to the wall; and

means for collecting the fines from the material which are suspendedproximate the top wall of the container.

References Cited UNITED STATES PATENTS 1,000,689 8/1911 Paterson 2594 XR2,718,471 9/1955 Samler 2594 XR 3,164,376 1/1965 Clark 2594

